Back light unit for backlit displays

1. A back light unit comprising: a) a plurality of light emitting diodes positioned on a substrate; and b) a plurality of flat lenses, a respective one of the plurality of flat lens being positioned a distance above a respective one of the plurality of light emitting diodes, each of the plurality of flat lenses comprising a plurality of annular segments having a common center, each of the plurality of annular segments comprising a prism shape microstructure having an exit facet having an angle with respect to a plane that is parallel to a plane of an emitting surface of respective ones of the plurality of light emitting diodes that is defined by the Fresnel equation and being configured to refract the light in a desired direction, and a facet oriented in the plane that is parallel to the plane of the emitting surface of respective ones of the plurality of light emitting diodes, and wherein a scaling factor of a height of each of the plurality of annular segments is in a range from 0.5 to 1.0, thereby providing a collimation of light exiting the plurality of flat lenses that exhibits a ratio of a difference in an angle where an intensity of exiting light at 10% of a maximum value and an angle where the intensity of exiting light is at 80% of the maximum value divided by an angle where the intensity of exiting light is at 50% of the maximum value that is greater than 0.7.

2. The back light unit of claim 1 wherein at least one of the plurality of flat lenses comprises a Fresnel lens.

3. The back light unit of claim 1 wherein a thickness of at least one of the plurality of flat lenses is between 45-55% of a spacing distance of the plurality of light emitting diodes.

4. The back light unit of claim 1 wherein a refractive index of at least one of the plurality of flat lenses is between 1.5 or 1.57.

5. The back light unit of claim 1 wherein at least one of the plurality of flat lenses is configured so that it collimates in one dimension with a FWHM of less than 40 degrees.

6. The back light unit of claim 1 wherein at least one of the plurality of flat lenses is configured so that it collimates in two dimensions with a FWHM of less than 40 degrees.

7. The back light unit of claim 1 wherein at least one of the plurality of flat lenses is configured to collimate asymmetrically.

8. The back light unit of claim 1 wherein at least one of the plurality of flat lenses is configured to provide the same collimation in all directions.

9. The back light unit of claim 1 wherein at least one of the plurality of flat lenses comprises disturbances superimposed on a surface that are configured to provide additional spreading in one dimension.

10. The back light unit of claim 1 wherein at least one of the plurality of flat lenses comprises disturbances superimposed on a surface that are configured to provide additional spreading in two dimensions.

11. The back light unit of claim 1 wherein at least one of the plurality of annular segments comprises a circular segment.

12. The back light unit of claim 1 wherein the exit facet of an inner-most one of the plurality of annular segments is positioned parallel to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

13. The back light unit of claim 1 wherein the exit facet of an outer-most one of the plurality of annular segments is positioned perpendicular to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

14. The back light unit of claim 1 wherein the common center of each of the plurality of annular segments of the plurality of flat lenses are vertically aligned to respective ones of centers of emission of the plurality of light emitting diodes.

15. The back light unit of claim 1 wherein at least some of the common centers of the plurality of annular segments of the plurality of flat lenses are spatially offset from centers of emission of the at least some of the respective ones of the plurality of light emitting diodes.

16. The back light unit of claim 1 wherein at least one of the plurality of light emitting diodes comprises an emitting area that is greater in one dimension.

17. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to diffuse light transmitting through the optical film, thereby improving visual uniformity.

18. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to spread light transmitting through the optical film in two dimensions to achieve a predetermined angular distribution.

19. The back light unit of claim 18 wherein the two dimensions are orthogonal dimensions.

20. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to equalize the angular distribution of the light transmitting through the optical film by incorporating a spatially varying angle bend.

21. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on one surface.

22. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on both a first surface and a second surface.

23. The back light unit of claim 22 wherein at least some of the microlenses on the first surface are different from some of the microlenses on the second surface.

24. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that minimizes crosstalk between dimming zones.

25. The back light unit of claim 1 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that enhances collimation by recirculating reflected light.

26. The back light unit of claim 1 further comprising a reflecting polarizer film positioned adjacent to the plurality of flat lens.

27. The back light unit of claim 1 wherein at least some of the plurality of flat lens are configured to collimate light generated by adjacent ones of the plurality of light emitting diodes in a Gaussian angular distribution.

28. A back light unit comprising: a) a plurality of light emitting diodes positioned on a substrate; and b) a plurality of flat lenses, a respective one of the plurality of flat lens being positioned a distance above a respective one of the plurality of light emitting diodes, each of the plurality of flat lenses comprising a plurality of annular segments having a common center, each of the plurality of annular segments comprising a prism shape microstructure having an exit facet configured to refract the light in a desired direction and a facet oriented in a plane that is parallel to a plane of an emitting surface of respective ones of the plurality of light emitting diode, wherein at least one of the plurality of flat lenses comprises disturbances superimposed on a surface that are configured to provide additional spreading in one dimension.

29. The backlight unit of claim 28 wherein the at least one of the plurality of flat lenses comprises disturbances superimposed on the surface that are configured to provide additional spreading in two dimensions.

30. The back light unit of claim 28 wherein at least one of the plurality of flat lenses comprises a Fresnel lens.

31. The back light unit of claim 28 wherein a thickness of at least one of the plurality of flat lenses is between 45-55% of a spacing distance of the plurality of light emitting diodes.

32. The back light unit of claim 28 wherein a refractive index of at least one of the plurality of flat lenses is between 1.5 or 1.57.

33. The back light unit of claim 28 wherein at least one of the plurality of flat lenses is configured so that it collimates in one dimension with a FWHM of less than 40 degrees.

34. The back light unit of claim 28 wherein at least one of the plurality of flat lenses is configured so that it collimates in two dimensions with a FWHM of less than 40 degrees.

35. The back light unit of claim 28 wherein at least one of the plurality of flat lenses is configured to collimate asymmetrically.

36. The back light unit of claim 28 wherein at least one of the plurality of flat lens is configured to provide the same collimation in all directions.

37. The back light unit of claim 28 wherein at least one of the plurality of annular segments comprises a circular segment.

38. The back light unit of claim 28 wherein the exit facet of an inner-most one of the plurality of annular segments is positioned parallel to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

39. The back light unit of claim 28 wherein the exit facet of an outer-most one of the plurality of annular segments is positioned perpendicular to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

40. The back light unit of claim 28 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined to match a spherical lens.

41. The back light unit of claim 28 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined using the Fresnel equation.

42. The back light unit of claim 28 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined using the Fresnel equation and subsequent scaling by a factor between 0.5 to 1.0.

43. The back light unit of claim 28 wherein the common center of each of the plurality of annular segments of the plurality of flat lenses are vertically aligned to respective ones of centers of emission of the plurality of light emitting diodes.

44. The back light unit of claim 28 wherein at least some of the common centers of the plurality of annular segments of the plurality of flat lenses are spatially offset from centers of emission of the at least some of the respective ones of the plurality of light emitting diodes.

45. The back light unit of claim 28 wherein at least one of the plurality of light emitting diodes comprises an emitting area that is greater in one dimension.

46. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to diffuse light transmitting through the optical film, thereby improving visual uniformity.

47. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to spread light transmitting through the optical film in two dimensions to achieve a predetermined angular distribution.

48. The back light unit of claim 47 wherein the two dimensions are orthogonal dimensions.

49. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to equalize the angular distribution of the light transmitting through the optical film by incorporating a spatially varying angle bend.

50. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on one surface.

51. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on both a first surface and a second surface.

52. The back light unit of claim 51 wherein at least some of the microlenses on the first surface are different from some of the microlenses on the second surface.

53. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that minimizes crosstalk between dimming zones.

54. The back light unit of claim 28 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that enhances collimation by recirculating reflected light.

55. The back light unit of claim 28 further comprising a reflecting polarizer film positioned adjacent to the plurality of flat lens.

56. The back light unit of claim 28 wherein at least some of the plurality of flat lens are configured to collimate light generated by adjacent ones of the plurality of light emitting diodes in a Gaussian angular distribution.

57. A back light unit comprising: a) a plurality of light emitting diodes positioned on a substrate; and b) a plurality of flat lenses, a respective one of the plurality of flat lens being positioned a distance above a respective one of the plurality of light emitting diodes, each of the plurality of flat lenses comprising a plurality of annular segments having a common center, each of the plurality of annular segments comprising a prism shape microstructure having an exit facet configured to refract the light in a desired direction and a facet oriented in a plane that is parallel to a plane of an emitting surface of respective ones of the plurality of light emitting diode, wherein at least some of the common centers of the plurality of annular segments of the plurality of flat lenses are spatially offset from centers of emission of the at least some of the respective ones of the plurality of light emitting diodes.

58. The back light unit of claim 57 wherein at least one of the plurality of flat lenses comprises a Fresnel lens.

59. The back light unit of claim 57 wherein a thickness of at least one of the plurality of flat lenses is between 45-55% of a spacing distance of the plurality of light emitting diodes.

60. The back light unit of claim 57 wherein a refractive index of at least one of the plurality of flat lenses is between 1.5 or 1.57.

61. The back light unit of claim 57 wherein at least one of the plurality of flat lenses is configured so that it collimates in one dimension with a FWHM of less than 40 degrees.

62. The back light unit of claim 57 wherein at least one of the plurality of flat lenses is configured so that it collimates in two dimensions with a FWHM of less than 40 degrees.

63. The back light unit of claim 57 wherein at least one of the plurality of flat lenses is configured to collimate asymmetrically.

64. The back light unit of claim 57 wherein at least one of the plurality of flat lens is configured to provide the same collimation in all directions.

65. The back light unit of claim 57 wherein at least one of the plurality of annular segments comprises a circular segment.

66. The back light unit of claim 57 wherein the exit facet of an inner-most one of the plurality of annular segments is positioned parallel to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

67. The back light unit of claim 57 wherein the exit facet of an outer-most one of the plurality of annular segments is positioned perpendicular to the plane of the emitting surface of the respective one of the plurality of light emitting diodes.

68. The back light unit of claim 57 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined to match a spherical lens.

69. The back light unit of claim 57 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined using the Fresnel equation.

70. The back light unit of claim 57 wherein an angle of the exit facet of at least one of the plurality of annular segments is determined using the Fresnel equation and subsequent scaling by a factor between 0.5 to 1.0.

71. The back light unit of claim 57 wherein the common center of each of the plurality of annular segments of the plurality of flat lenses are vertically aligned to respective ones of centers of emission of the plurality of light emitting diodes.

72. The back light unit of claim 57 wherein at least one of the plurality of flat lenses comprises disturbances superimposed on a surface that are configured to provide additional spreading in one dimension.

73. The back light unit of claim 57 wherein at least one of the plurality of flat lenses comprises disturbances superimposed on a surface that are configured to provide additional spreading in two dimensions.

74. The back light unit of claim 57 wherein at least one of the plurality of light emitting diodes comprises an emitting area that is greater in one dimension.

75. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to diffuse light transmitting through the optical film, thereby improving visual uniformity.

76. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to spread light transmitting through the optical film in two dimensions to achieve a predetermined angular distribution.

77. The back light unit of claim 76 wherein the two dimensions are orthogonal dimensions.

78. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film is configured to equalize the angular distribution of the light transmitting through the optical film by incorporating a spatially varying angle bend.

79. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on one surface.

80. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a plurality of microlenses formed on both a first surface and a second surface.

81. The back light unit of claim 80 wherein at least some of the microlenses on the first surface are different from some of the microlenses on the second surface.

82. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that minimizes crosstalk between dimming zones.

83. The back light unit of claim 57 further comprising an optical film positioned between the plurality of flat lenses and the plurality of light emitting diodes, wherein the optical film comprises a light absorbing material that enhances collimation by recirculating reflected light.

84. The back light unit of claim 57 further comprising a reflecting polarizer film positioned adjacent to the plurality of flat lens.

85. The back light unit of claim 57 wherein at least some of the plurality of flat lens are configured to collimate light generated by adjacent ones of the plurality of light emitting diodes in a Gaussian angular distribution.